Surface semiconductor optical amplifier with transparent substrate

ABSTRACT

A surface-type light amplifier device has an active layer ( 13 ) of a light amplification section ( 11 ) sandwiched between an n-type semiconductor cladding layer ( 12 ) that is an n-type semiconductor layer and a p-type semiconductor multilayer reflecting mirror ( 14 ). The light amplification section is attached to a transparent substrate ( 21 ) on the side of the n-type semiconductor cladding layer. A plurality of divided electrodes ( 16 ) form electrical continuity relative to the p-type semiconductor multilayer reflecting mirror via a p-type cap layer ( 15 ) provided on the reflecting mirror. An electrode ( 18 ) forming electrical continuity relative to the n-type semiconductor cladding layer is connected to a wiring conductor ( 20 ) provided on the surface of the transparent substrate. The device enables amplification of a single, uniform, large-diameter light beam and oscillation of a laser.

BACKGROUND OF THE INVENTION

1. Field of the Invention;

The present invention relates to a surface-type light amplifier deviceusable as a surface light emitting laser etc. when a resonator isdisposed outside the device and to a method for the manufacture thereof.The “surface-type” light amplifier device referred to herein is a devicecomprising a light function portion for amplifying and emitting lightand a substrate for physically supporting the light amplificationfunction portion, wherein the emitted light rises with a specific anglerelative to the surface of the substrate, generally in the direction ofintersecting the substrate surface at right angles (in the normaldirection).

2. Discussion of the Background

As for surface-type light amplifier devices of this type, there is onedisclosed in Reference Literature 1. “Electrically pumped mode-lockedvertical-cavity semiconductor lasers” (W. Jiang, IM. Shimizu, R. P.Miin, T. E. Reynolds and J. E. Bowers, Optics Letters, Vol. 18, No. 22,pp. 1937-1939, 1993). As shown in FIG. 2, the prior art surface-typelight amplifier device 30 structurally comprises an n-type GaAssubstrate 31 on which a multilayer reflecting mirror of n-typesemiconductor 32, an n-type cladding layer 33, an n-type GaAs activelayer 34, a p-type cladding layer 35, a p-type AlGaAs layer 37 and ap-type GaAs contact layer 38 are deposited in the order mentioned. Thep-type AlGaAs layer 37 and p-type GaAs contact layer 38 are partiallycut off into a shape having a shape having a predetermined surface area.An antireflection coating 39 is deposited onto the top surface of thep-type GaAs contact layer. A surface electrode 40 is formed on thep-type cladding layer 35, with an insulating film 36 sandwichedtherebetween, so as to surround the cut-off portions and come intocontact with the top peripheral part of the p-type GaAs contact layer38. A substrate electrode 41 is deposited on the bottom surface of then-type substrate 31.

Injection of carriers into the n-type GaAs active layer 34 is attainedby current injection, i.e. by applying voltage between the surfaceelectrode 40 and the substrate electrode 41.

Holes are injected from the surface electrode 40 into the n-type GaAsactive layer 34 sequentially via the p-type GaAs contact layer 38,p-type AlGaAs layer 37 and p-type cladding layer 35. Electrons areinjected from the substrate electrode 41 into the n-type Gas activelayer 34 sequentially via the n-type GaAs substrate 31, multilayerreflecting mirror of n-type semiconductor 32 and n-type cladding layer33.

When the prior art device 30 is used as a light amplifier device orparticularly as a surface-emitting laser, the associated resonatorcomprises the multilayer reflecting mirror of n-type semiconductor 32built in the device and an external reflecting mirror (not shown).Between the external reflecting mirror not shown and the antireflectioncoating 39 there is generally disposed a lens (not shown). It goeswithout saying that the antireflection coating 39 is used for reducingthe resonator loss and obtaining the light gain. For the same reason,the layers 33 to 35, 37 and 38 are subjected to treatments such as forsuppressing the impurity concentration etc. to a low degree so that theoptical absorption loss can be lowered.

FIG. 3 shows another prior art surface-type light amplifier device 50.This device is disclosed in Reference Literature 2: “Highsingle-transverse-mode output from external-cavity surface-emittinglaser diode” (M. A. Hadley, G. C. Wilson, K. Y. Lau and J. S. Smith,Appl. Phys. Lett., Vol. 63, No. 12, pp. 1607-1609, 1993) and comprises aGaAs substrate 51 not of n-type but of p-type, on which a multilayerreflecting mirror 52 of p-type. semiconductor, a p-type multi-quantumwell active region 53 and a multilayer reflecting mirror 55 of n-typesemiconductor are deposited in the order mentioned. Voltage is appliedbetween a substrate electrode 57 deposited on the bottom surface of thesubstrate 51 and a bonding pad 56 :disposed on an insulating film 54 andbrought into contact with the top peripheral surface of the multilayerreflecting mirror of n-type semiconductor 55 to inject an electriccurrent (carriers) into the multi-quantum well active region 53, therebyobtaining excited light. Holes are injected from the side of thesubstrate electrode 57 into the multi-quantum well active layer 53 viathe p-type GaAs substrate 51 and the multilayer reflecting mirror ofp-type semiconductor 52, whereas electrons are injected thereinto fromthe opposite side, i.e. from the bonding pad 56, via the multilayerreflecting mirror of n-type semiconductor 55.

This device 50 is, by nature, not a device for an external resonator.However, in the case that a resonator is composed only of the multilayerreflecting mirror of n-type semiconductor 55 and the multilayerreflecting mirror of p-type semiconductor 52 embedded in the device, itinevitably poses a substantial problem that the transverse mode does notbecome a single lobe when the diameter of the device is made large. Inorder to solve the problem it is necessary to provide an externalreflecting mirror not shown. Single-lobe beams can be obtained bydeliberately lowering the reflectivity of the multilayer reflectingmirror of n-type semiconductor 55, then providing a suitable reflectingmirror outside the device on the side of the multilayer reflectingmirror of n-type semiconductor 55, and adjusting the position of a lensdisposed in an optical path toward the external reflecting mirror, forexample. In any event, the resonator has a composite constructioncomprising a first resonator composed of the multilayer reflectingmirror of p-type semiconductor 52 and the multilayer reflecting mirrorof n-type semiconductor 55 which are provided in the device and a secondresonator composed of the multilayer reflecting mirror of p-typesemiconductor 52 and the external reflecting mirror.

In the device 30 shown in FIG. 2, however, it is particularly difficultto obtain laser beams having a large diameter. This is because, if theeffective area of the n-type GaAs active layer 34, i.e. the area coatedwith the antireflection coating 39 and actually contributing tooscillation, is made large for enlarging the device diameter, it willbecome impossible to uniformly inject holes into that area. This resultssolely from the fact that each of the p-type semiconductor layers 38, 37and 35 has high electrical resistance. In order to inject holes into theneighborhood of the center of the effective area of the n-type GaAsactive layer, it is necessary to cause the holes first to flow throughthe p-type semiconductor layers 38, 37 and 35 in the in-plane directionfrom the surface electrode 40 in contact with the peripheral edge of theantireflection coating 39 and then to be injected into the center of then-type GaAs active layer 34. In the actual course of operation, however,this cannot be attained because the majority of holes are injected intothe peripheral edge of the p-type GaAs contact layer 38 from the surfaceelectrode 40 and then advance straightforward without being well spreadlaterally and reach the n-type GaAs active layer 34.

In order to actually secure the state of uniform hole injection into then-type GaAs active layer 34 in the conventional device 30 fabricated inaccordance with such structural principle, it is required to reduce thediameter of the effective area of the n-type GaAs active layer 34 to notmore than tens of μm. That is to say, when a large output power isrequired, it is necessary to adopt a method of arraying a plurality ofdevices, resulting in sacrifices of singleness and uniformity of opticalbeams.

In the conventional device 50 shown in FIG. 3, however, since holes canbe injected from the substrate electrode 57 in surface contact with theback surface of the p-type GaAs substrate 51, the uniformity in thein-plane distribution of holes injected into the p-type multi-quantumwell active region 53 will be satisfied. However, the serious problem isthat the device has a composite resonator structure which cannotconstitute a pure external resonator type surface light emitting laserand since the multilayer reflecting mirror of n-type semiconductor 55incorporated in the device generally has a reflectance of not less thanabout 80%, the device is not suitable as a surface-type light amplifierdevice. In addition, due to the composite resonator structure, lightpulses cannot be generated in the mode-locking operation.

Furthermore, since the multilayer reflecting mirror of n-typesemiconductor 55 having a resistance lower than that of a p-type one isused for the sake of electron flow in the in-plane direction, thestructure is designed for injecting electrons into the neighborhood ofthe center of the multi-quantum well active region 53. However, if thediameter of the multi-quantum well active area 53 is set larger, theelectrical resistance of the multilayer reflecting mirror of n-typesemiconductor 55 cannot be ignored and unevenness in the currentinjection is induced. That is to say, for uniform current injection, theupper limit of the effective area of the multi-quantum well active area53 is about 100 μm in diameter though it is larger than that of theconventional device 30 shown in FIG. 2. In particular, it is impossibleto control the injection of holes into the active layer because thep-type electrode is the substrate electrode and an electric current isinjected through the substrate.

SUMMARY OF THE INVENTION

The present invention has been proposed in view of the problemsmentioned above, and its object is to provide a surface-type lightamplifier device having at least a light amplification section includinga structure of an active layer sandwiched between p-type and n-typecladding layers and emitting a light beam in the direction rising with aspecific angle (generally, 90° as stated above) relative to the surfaceof a support substrate, wherein the amplification of a single anduniform light beam or, if required, a large-diameter light beam, and thelaser oscillation can be attained.

The inventor believes that, in the final analysis, the various drawbacksof the conventional devices 30 and 50 shown in FIGS. 2 and 3 result fromthe presence per se of the n-type substrate 31 or the p-type substrate51 forming the light amplification section contributing to the lightamplification, namely, the multilayer structure including thesemiconductor layers 32-35 and 37-38 in the device 30 shown in FIG. 2 orthe multilayer structure including the semiconductor layers 52, 53 and55 in the device 50 shown in FIG. 3.

It goes without saying that the substrate 31 or 51 is indispensable tothe formation of the light amplification section and important evenafter the section has been formed as a support for securing the physicalstrength of the device. Insofar as the light amplifying function isconcerned, however, the substrates 31 and 51 are rather unnecessary orobstructive. Since the substrates 31 and 51 generally have a largethickness of up to hundreds of μm, when a compound semiconductorsubstrate such as a GaAs substrate is employed, loss in passingamplified light therethrough is very large.

For this reason, both the conventional devices 30 and 50 shown in FIGS.2 and 3 have a construction such that amplified light is not passedthrough the support substrates 31 and 51. This is the same in otherconventional devices not touched upon here. In other words, variouschanges in construction for improving the characteristics of deviceshave heretofore had to be made on the major premise that light shouldnot be passed through a substrate. This has brought about variousrestrictions. In the case of the conventional device 30 shown in FIG. 2,for example, since the light emitted from the light amplificationportion has to be emitted from the side of the p-type semiconductorlayers 35, 37 and 38 opposite the side at which the n-type GaAssubstrate 31 is present, this light emitting surface cannot be coveredby the electrode. As a result, an electric current has to be appliedonly through the peripheral edge of the p-type AlGaAs layer 37 to thethe p-type cladding layer and then to the n-type GaAs active layer 34 asdescribed above, thereby inducing the aforementioned uneven holeinjection and difficulty in achieving a large device diameter.

In the case of the conventional device 50 shown in FIG. 3, the p-typeGaAs substrate 51 is used in place of the n-type GaAs substrate, withthe result that there is an advantage that the multilayer reflectingmirror of n-type semiconductor 55 can be disposed on the side oppositethe side at which the substrate is present to achieve low resistance,but there are restrictions, such as requiring a composite resonancestructure, resulting in the different drawbacks as described above.Disclosure of the Invention:

In view of the above, the present inventor, exploding thewell-established concept, has conceived the idea of removing a basesubstrate used for fabricating a light amplification section after thefabrication of the light amplification section. However, since the lightamplification section is an extremely thin structure, such mere removalof the base substrate would decrease the strength of the lightamplification section resulting in physical distortion producing opticaldistortion, and would not allow the light amplification section to beput into practical use. Therefore, the present invention provides astructure having the light amplification section attached to atransparent support substrate that is separate from the base substrateused in fabricating the light amplification section and exhibits a lowloss when a light beam passes therethrough.

With this device structure, a light beam amplified at the lightamplification section can be passed through the transparent substrate.This means that there arises a degree of freedom in structural design.For example, an electrode through which holes are injected into a p-typesemiconductor layer with relatively high resistance can be made large.Furthermore, even when a plurality of divided electrodes are formed anda light beam is prevented from being emitted from the side of theseelectrodes as in the specific embodiment of the present invention whichwill be described later, various improvements can be realized byenabling a light beam to be emitted via the transparent substrateprovided on the opposite side of the electrodes with the active layer ofthe light amplification section therebetween.

The present invention also provides a surface-type light amplifierdevice, as a preferred unsophisticated embodiment satisfying the abovefundamental conditions, having a light amplification section attached toa transparent substrate on the side on which an n-type seniconductorlayer is present and having a plurality of divided electrodes providedon the side across an active layer opposite the n-type semiconductorlayer for injecting holes into a p-type semiconductor layer.

In this surface-type light amplifier device, it is possible to uniformlyinject holes into the p-type semiconductor layer having higherresistance than an n-type one. In addition, since the in-planedistribution of the carriers in the active layer can be controlled bycontrolling the amount of an electric current applied to the dividedelectrodes, it is possible to control the in-plane distribution toconform to the light intensity distribution in the fundamental modehaving a single lobe.

The present invention provides, as a more concrete unsophisticatedembodiment, a surface-type light amplifier device wherein an activelayer in a light amplification section is sandwiched between an n-typesemiconductor cladding layer that is an n-type semiconductor layer and ap-type semiconductor multilayer reflecting mirror that is a p-typesemiconductor layer; the light amplification section is attached to atransparent substrate on the side of the n-type semiconductor claddinglayer; a plurality of divided electrodes attain electric continuitythrough a p-type cap layer provided on the p-type semiconductormultilayer reflecting mirror; and an electrode forming electricalcontinuity, relative to the n-type semiconductor cladding layer isconnected to a wiring conductor provided on the transparent substrate.

The present invention further provides a method for fabricating asurface-type light amplifier device, which includes the steps of forminga light amplification section on a structural substrate for theformation of that section, attaching a different transparent substrateto the exposed surface of the light amplification section, and removingthe structural substrate.

As an unsophisticated embodiment of the aforementioned fabricationmethod, the present invention provides a fabrication method comprisingthe steps of successively forming a p-type semiconductor layer, anactive layer and an n-type semiconductor layer in the order mentioned onthe structural substrate, attaching the transparent substrate to theexposed surface of the n-type semiconductor layer, and forming aplurality of divided electrodes on the surface of the p-typesemiconductor layer exposed after the removal of the structuralsubstrate, thereby attaining electrical continuity relative to thep-type semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1(A) is a schematic view showing the configuration of one exampleof a surface-type light amplifier device according to the presentinvention,

FIG. 1(B) an explanatory view showing the process for fabricating thesurface-type light amplifier device according to the present invention,

FIG. 2 a schematic view showing the configuration of one typical exampleof a conventional surface-type light amplifier device, and

FIG. 3 another typical example of a conventional surface-type lightamplifier device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference tothe accompanying drawings.

FIG. 1(A) shows a schematic configuration of one example of surface-typelight amplifier device 10 fabricated in accordance with the presentinvention. In the present invention, a light amplification section 11including a structure of sandwiching between p-type and n-typesemiconductor layers 14 and 12 an active layer 13 that produces excitedcarriers is attached by means of a transparent adhesive 22 to atransparent substrate 21 that differs from a structural substrate onwhich the light amplification section 11 has been formed. That is tosay, FIG. 1(A) shows the state in which the structural substrate hasbeen removed.

In the device 10 of the present invention thus configured, since a lightbeam produced at the light amplification section 11 can pass through thetransparent substrate 21, the degree of freedom for constructionalimprovements in this section 11 increases. As described below, FIG. 1(A)discloses the configuration in one preferred unsophisticated embodimentin accordance with the present invention. However, there can be providedother various surface-type light amplifier devices in accordance withthe fundamental construction of the present invention. The material forthe transparent substrate 21 may be glass, plastic, etc. having veryhigh transparency with respect to the oscillation wavelength. From thesematerials can be easily obtained one having transmittance of 99 to 99.9%with respect to transmission beams in the optical wavelength range. Itis noted, however, that the larger the thickness, the larger thetransmission loss even when the transmission is markedly high.Generally, however, the thickness of the substrate that can physicallysupport the light amplification section 11 thereon and can ensure astrength thereof large enough to prevent the section from distortionfalls in the range of hundreds of μm to several mm, in which range thetransparency is fully satisfactory.

As the transparent adhesive 22 commercially available polyimide etc. canbe used. Since such an adhesive agent has sufficiently hightransmittance and is used in the form of a thin film, there arises noproblem in use. Surface levelling (optical precision) of the transparentsubstrate 21 and uniform application of the transparent adhesive 22 canbe satisfactorily attained with easel using any prior art technology. Inorder to avoid diffused reflection on the surface of the transparentsubstrate 21, the interface between the transparent substrate 21 and thetransparent adhesive 22 and the interface between the transparentadhesive and the light amplification section 11, antireflection coatings25, 24 and 23 are applied beforehand to. these faces. The antireflectioncoatings can be constituted of a double-layer laminate structure of TiO₂and SiO₂.

In the surface-type light amplifier device 10 of the present inventionas shown in FIG. 1(A), the concrete construction of the lightamplification section 11 is as follows. Attached through the transparentadhesive 22 and antireflection coating 23 to the transparent substrate21 is an n-type cladding layer 12 that can be constituted, for example,of an n-type Al_(x)Ga_(1−x)As (x=0.3) layer having a thickness of about2 μm.

On that layer is formed an active layer 13 that is the principal part ofthe light amplification section 11 and is constituted of a non-dopedGaAs layer having a thickness of about 0.5μm.

On the active layer 13 is formed a p-type semiconductor multilayerreflecting mirror 14 that is a p-type semiconductor layer and isconstituted, for example, of a periodical repetition laminate structureof an Al_(x)Ga_(1−x)As (x=0.1) layer and a p-type AlAs layer. Each layerhas a considerably small thickness, and the total thickness of thestructure. is approximately several μm. However, since such asemiconductor multilayer reflecting mirror per se is well known, it canbe produced in accordance with an optional prior art technology.

As will be understood from the fact that a semiconductor multilayerreflecting mirror 14 is used as a p-type semiconductor layer in thesurface-type light amplifier device 10 shown in FIG. 1(A), the devicehas a structure such that a light beam produced at the active layer 13is reflected by the reflecting mirror 14 and is radiated to an exteriorspace through the n-type cladding layer 12 and transparent substrate 21.Therefore, unlike the conventional device of FIG. 3 relying on thecomposite resonator structure constructed together with a resonatorbuilt in the device, it is possible to provide a complete unit ofexternal reflecting mirror type light emitting laser, though not shown,by disposing a commercially available high-performance reflectingmirror, e.g. a planar dielectric multilayer reflecting mirror havingreflectivity of not less than 99%, in an exterior space on an extensionof the emission path of the light beam while interposing a suitable lensbetween the device and the mirror, if necessary.

In order to produce excited carriers in the active layer 13, it isrequired to inject an electric current into the active layer 13. Theconstitution for this requirement is as described hereinafter, wherein aparticularly effective arrangement is adopted.

On the p-type semiconductor multilayer reflecting mirror 14 is formed ap-type GaAs cap layer 15 having a thickness of 3000 Å and doped withhigh-concentration Zn. The particularly effective arrangement is that aplurality of divided electrodes 16 for hole injection are provided onthe cap layer. In the embodiment shown in FIG. 1, the electrodes: 16comprise a disc-shaped electrode at the center and a plurality ofring-like electrodes concentric with the center electrode and arrangedat prescribed intervals. With this structure, the in-plane distributionof holes injected from the electrodes into the active layer via thep-type cap layer 15 and p-type semiconductor multilayer reflectingmirror 14 can be controlled to be uniform by controlling voltage appliedto the individual electrodes, and active control can be made in theoperation of the device.

That is to say, while, in the conventional device, the hole flow througha very thin p-type semiconductor layer with high resistance into anactive layer is deviated, resulting in an obstacle to uniform holeinjection, the structure shown in the drawing makes it possible not onlyto inject holes uniformly into the active layer 13, but also to controlthe injection current distribution more positively to obtain a gaindistribution suitable for a light distribution of an oscillation modeetc. When a light distribution of the fundamental mode having a singlelobe is to be obtained, for example, the amounts of an electric currentto be injected into the electrodes are set higher toward the centralelectrode; It is further possible to obtain a stable and highly preciselasing light, a lasing light beach of a desired far-field pattern, etc.

The divided electrodes 116 are not limited to the concentric ones asshown in FIG. 1, but can optionally be selected from a pattern of stripsarranged in parallel, a predetermined plane pattern of dots each ofcircular, rectangular shape or the like, and other patterns.

On the other hand, the electrode for injecting electrons into the n-typesemiconductor layer 12 with relatively low resistance can be formed moresimply. In FIG. 1, a ring-like contact layer 17 in contact with thebottom surface of the n-type semiconductor layer (cladding layer) 12 isformed along the outer periphery of the light amplification section 11formed into a predetermined solid (cylindrical shape in the drawing) asa whole, and an electrode 18 of an alloy of AuGe or the like formed onthe contact layer is electrically connected via an electrode connectingmember 19 to a wiring conductor 20 formed on the surface of thetransparent substrate 12 around the light amplification section 11. Thecontact layer 17 has a thickness of about 1000 Å and can be constitutedof an n-type GaAs layer, for example. The electrode connecting member 19can be constituted of a solder of In or AuSn. The wiring conductor 20can be constituted of Au or the like.

As mentioned briefly earlier, when the device shown in the drawing isused as an external resonator type surface light emitting laser, aresonator can be constituted of the p-type semiconductor multilayerreflecting mirror 14, and an external reflecting mirror and a lens whichare not shown in the drawing. The lens is disposed in an exterior spaceopposite the active layer 13 on the side of the transparent substrate21, and the external reflecting mirror is disposed on an extension of aline connecting the transparent substrate 21 and the lens. That is tosay, the surface-type device 10 is disposed so that the substrate 21faces the external reflecting mirror with the lens interveningtherebetween. The device, lens and external reflecting mirror are placedon a fine-motion table capable of optical adjustment. The externalreflecting Mirror is a planar-type reflecting mirror that reflects lighthaving an emission wavelength at sufficiently high reflectivity, e.g. adielectric multilayer reflecting mirror having reflectivity of not lessthan 99%.

The light reflected by the p-type semiconductor multilayer reflectingmirror 14 is amplified again in the area of the active layer 13,collimated by the lens, reflected again by the external reflectingmirror, and returned to the active layer 13 and to the p-typesemiconductor reflecting mirror 14. This sequence is repeated to giverise to laser oscillation. At this time, an adjustment mechanism such asthe fine-motion table is used to optically adjust the device, lens andexternal reflecting mirror so as to reduce resonator loss. The distancebetween the external reflecting mirror and the device, i.e. the externalresonator length, is made sufficiently small. This is for avoiding theinfluence of vibration etc.

An electric current is applied to the divided electrodes 16 so as to bematched with the light intensity distribution in the fundamental mode ofsingle lobe, namely so that it flows mostly through the centerelectrode. By this, it is possible to realize an external resonator-typesurface light emission laser with a large output. In addition, theelectric current applied to the divided electrodes 16 is suitablymodulated for the round-trip time of light passing through the length ofthe external resonator, e.g. modulated at 1 GHz where the round-triptime of light is 1 ns, with the result that an active mode-lockingoperation is assumed to enable generation of light pulses.

The surface-type light amplifier devices according to the presentinvention, inclusive of the one designated by 10 shown in FIG. 1(A), canbe fabricated by various methods. However, a desirable process forfabricating the device 10 shown in FIG. 1(A) can be exemplified in FIG.1(B). As shown at step 101, a commercially available GaAs substratehaving a thickness of approximately 400 μm is used as a substrate forconstructing a light amplification section, and on the substrate isformed an Al_(x)Ga_(1−x)As layer (x=0.6) having a thickness of around3000 Å that functions as an etching prevention layer in a subsequentetching step.

On the etching prevention layer is constructed the light amplificationsection 11 of FIG. 1(A), in an inverted state, as shown at step 102.Therefore, the divided electrodes 16 cannot be formed at this step. Tobe specific, the p-type cap layer 15, p-type semiconductor multilayerreflecting mirror 14, active layer 13, n-type cladding layer 12 andcontact layer 17 are successively deposited in the order mentioned. Thelight amplification section 11 in a predetermined three-dimensionalshape such as a columnar shape is formed by using a deposition techniqueand lithography or a like technique together. Lithography is similarlyutilized to remove part of the contact layer 17 present at the beampassageway and exhibiting a large optical loss. The antireflectioncoating 23 is further formed when found necessary by using a coatingtechnique and lithography together.

As shown at subsequent step 103, to the side of the n-type claddinglayer 12 exposed to the outside, namely to the side of theantireflection coating 23 when formed, is attached a transparentsubstrate 21, such as of glass, having a highly flat surface via thetransparent adhesive of polyimide or the like applied uniformly ontothat side.

The physical strength of the light amplification section 11 is thussecured beforehand so as not to induce any physical or opticaldistortion. The thus constructed structure is then subjected to asubstrate polishing step. Since the substrate is as thick as about 400μm as shown above, it is polished as shown at step 104 using amechanical polishing method so that the resultant thickness isapproximately 30 to 100 μm.

After the substrate has been polished to have such a thickness, it isetched at an appropriate temperature with a suitable solution, e.g. atabout 20° C. with a mixed solution of one part of ammonia and twentyparts of a hydrogen peroxide solution as shown at step 105. When theaforementioned Al_(x)Ga_(1−x)As layer (x=0.6) has been formed as anetching prevention layer on the substrate, the substrate can be etchedup to the etching prevention layer at high speed of about 20 μm/minwithout strictly managing the etching time, and it is possible to stopthe etching. As the etching prevention layer, an AlAs layer or the likecan also be used.

As shown at subsequent step 106, the etching prevention layer is removedby etching it with a mixed solution of phosphoric acid, a hydrogenperoxide solution and water (H₃PO₄:H₂O₂:H₂O=3:1:50) at about 20° C.Since this etching is effected at a speed of about 1000 Å/min., theetching prevention layer can be easily removed under time management.

When the surface of the p-type cap layer 15 of the light amplificationsection 11 has been exposed to the outside, a predetermined number ofdivided electrodes 16 for injection of holes are formed in apredetermined pattern of arrangement as shown at step 107 by depositingan alloy of AuZn or the like onto the entire surface of the cap layerand then effecting lithography, or by using a printing technique after apredetermined pattern.

The electrical structural parts 17 to 20 to be formed on the n-typesemiconductor layer (cladding layer) 12 not described in detail hereinabove can be fabricated by a known method comprising suitable steps.

Although a preferred embodiment has been described in the foregoing, anymodification can be made therein insofar as it does not depart from thegist of the present invention. In addition to AlGaAs used as thematerial for the light amplification section 11, InGaAsP, GaN, etc. thatsimilarly fall under Group III-V semiconductors and photo-semiconductormaterials such as ZnSe that fall under Group II-VI semiconductors canalso be used.

According to the present invention, since the substrate used forconstructing a light amplification section can be removed and sincelight can be transmitted through a transparent substrate, the degree offreedom with respect to improvements in the light amplification sectionincreases to a great extent.

When an electrode for injection of holes to be provided on the side of ap-type semiconductor layer is composed f a plurality of dividedelectrodes in accordance with the preferred embodiment of the presentinvention, the amount of an electric current applied to each of thedivided electrodes can be controlled to enable carrier distribution inan active layer to be actively controlled. As a consequence, it ispossible to inject carriers in accordance with light intensitydistribution in the fundamental mode having a single lobe whenfabricating an external resonator-type surface light emitting laser toenable the operation in the fundamental mode to be stabilized.

Furthermore, when the side of the transparent substrate is used as alight emitting side, the p-type semiconductor functions as a multilayerreflecting mirror. For this reason, due to the optical stability of thep-type multilayer reflecting mirror obtained by fixing it to thetransparent substrate, the range of effective active region can beenlarged to materialize a current injection-type external resonator-typesurface light emitting laser with a large output, la light beamreflecting-type amplifier with a large diameter, etc. It is fullypossible to achieve generation of a light beam having a diameter ofseveral hundreds of μm or more. It goes without saying that since thesurface-type light amplifier device of the present invention is of acurrent injection type, an external-resonator active-mode lockingsurface light emitting laser can be materialized. In this case, a highoutput of light pulses can be generated.

What is claimed is:
 1. A surface-type light amplifier device having alight amplification section comprising: a p-type semiconductor layer; an-type semiconductor layer; and an active layer sandwiched between thep-type semiconductor layer and the n-type semiconductor layer forproducing excited carriers and emits a light beam in a direction risingat a specific angle relative to a surface of a support substrate,wherein said n-type semiconductor layer is attached to a transparentsubstrate different from a substrate for fabricating said lightamplification section, said n-type semiconductor layer serves as an-type semiconductor cladding layer and said p-type semiconductor layerserves as a p-type semiconductor multilayer reflecting mirror, saidlight amplification section is attached to said transparent substrate ona side of said ntype semiconductor cladding layer, and a light beamemitted from said active layer is transmitted through said transparentsubstrate.
 2. A surface-type light amplifier device according to claim1, wherein said light amplification section is attached to thetransparent substrate on a side of said n-type semiconductor layer,further comprising: an electrode for injection of holes formed on saidp-type semiconductor layer opposite said n-type semiconductor layer withsaid active layer intervening therebetween, wherein said electrodeincludes a plurality of divided electrodes arranged perpendicular to alight-advancing direction.
 3. A surface-type light amplifier deviceaccording to claim 2, wherein said plurality of divided electrodesattain electric continuity through a p-type cap layer provided on saidp-type semiconductor multilayer reflecting mirror, and wherein anelectrode electrically connects the n-type semiconductor cladding layerto a wiring conductor provided on said transparent substrate.